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Re: GCC optimizes integer overflow: bug or feature?
On 2006-12-21 17:42:15 -0500, Robert Dewar wrote:
> Marcin Dalecki wrote:
>
> >Of course I didn't think about a substitute for ==. Not! However I think
> >that checks for |x-y| < epsilion, could be really given a significant
> >speed edge
> >if done in a single go in hardware.
>
> One thing to ponder here is that "thinks" like this are what lead
> to CISC instruction messes. It just seems obvious to people that
> it will help efficiency to have highly specialized instructions,
> but in practice they gum up the architecture with junk, and a
> careful analysis shows that the actual gain is small at best.
> How many applications spend a significant amount of time doing
> such an epsilon test -- best guess: none.
Indeed, no-one has requested for one in the revision of IEEE 754,
AFAIK.
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Vincent Lefèvre <vincent@vinc17.org> - Web: <http://www.vinc17.org/>
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Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)